AFAIK, that was only an issue with the rotary engines, which tended to spray oil. Those engines looked like the later radial engines, but instead of being mounted to the airframe and turning a shaft attached to a propellor, the shaft was mounted to the airframe and the propeller attached to the engine, which itself spun at high speed. Good for air cooling, and the engines had very good horsepower-to-weight ration for the day, but they were problematic. The spinning engine introduced tremendous gyroscopic effects and the torque had interesting effects on flight dynamics. A turn to the right in a Sopwith Camel was incredibly tight, almost viciously so. A turn to the left was much more leisurely, dangerously so in a dogfight. They had no real throttle. It was almost a choice between full power and no power. To cut power for landing, there was a 'blipper' switch that cut power from the magneto, effectively turning off the engine. The problem was that fuel continued to flow, so you couldn't do this for very long or you risked an engine fire when you restored power to the spark plugs. That was very often bane in a wood and doped canvas plane. The starting, stopping, starting sound of "an engine in trouble" that was a staple in old, old movies was just standard procedure for landing a rotary-engined WWI fighter, misunderstood or misrepresented by Hollywood for dramatic effect. And all the castor oil flung by those spinning engines guaranteed that no pilots were ever constipated...